Stabilization of the Kelvin‐Helmholtz instability by the transverse magnetic field in the Magnetosphere‐Ionosphere Coupling System

Miura, Akira

doi:10.1029/96gl00598

Cited by 17 publications

(14 citation statements)

References 12 publications

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“…Although an abundance of heavy ions will affect the instability, heavy ions should primarily dampen the growth rates as they lead to a substantially broadened velocity shear region. The high growth rates are better explained, as predicted by the magnetohydrodynamic simulations of Miura and Kan [1992] and Miura [1996], by the lack of a conducting layer at the surface of the planet that can dissipate wave energy.…”

Section: Discussionmentioning

confidence: 91%

MESSENGER orbital observations of large‐amplitude Kelvin‐Helmholtz waves at Mercury's magnetopause

et al. 2012

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[1] We present a survey of Kelvin-Helmholtz (KH) waves at Mercury's magnetopause during MESSENGER's first Mercury year in orbit. The waves were identified on the basis of the well-established sawtooth wave signatures that are associated with nonlinear KH vortices at the magnetopause. MESSENGER frequently observed such KH waves in the dayside region of the magnetosphere where the magnetosheath flow velocity is still subsonic, which implies that instability growth rates at Mercury's magnetopause are much larger than at Earth. We attribute these greater rates to the limited wave energy dissipation in Mercury's highly resistive regolith. The wave amplitude was often on the order of 100 nT or more, and the wave periods were $10-20 s. A clear dawn-dusk asymmetry is present in the data, in that all of the observed wave events occurred in the postnoon and duskside sectors of the magnetopause. This asymmetry is likely related to finite Larmor-radius effects and is in agreement with results from particle-in-cell simulations of the instability. The waves were observed almost exclusively during periods when the north-south component of the magnetosheath magnetic field was northward, a pattern similar to that for most terrestrial KH wave events. Accompanying plasma measurements show that the waves were associated with the transport of magnetosheath plasma into the magnetosphere.

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Section: Discussionmentioning

confidence: 91%

MESSENGER orbital observations of large‐amplitude Kelvin‐Helmholtz waves at Mercury's magnetopause

et al. 2012

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“…Some other factors are not cover by our current model with ideal MHD theory, e.g., Hall term of the MHD equations [ Huba , 1994; Thomas , 1995], and finite Larmor radius term [ Huba , 1996]. The contribution of ionosphere is not addressed, while Galinsky and Sonnerup [1994] and Miura [1996]have shown that the sufficiently large Pederson conductivity can slow down the development of the K‐H instability. More work is needed to improve the model and the understanding of the K‐H instability in the future.…”

Section: Discussionmentioning

confidence: 99%

Spatial distribution of Kelvin‐Helmholtz instability at low‐latitude boundary layer under different solar wind speed conditions

Guo

Wang

2012

J. Geophys. Res.

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Using the PPMLR‐MHD global simulation model, we examined the Kelvin‐Helmholtz (K‐H) instability at the low‐latitude boundary layer (LLBL) under northward interplanetary magnetic field (IMF) conditions with various solar wind speeds (400, 600, and 800 km/s). The spatial distribution of the K‐H wave power in the equatorial plane shows two distinct power populations, referring to the two modes of K‐H surface waves. The spatial evolution of K‐H instability at the boundary layer is classified into four phases: quasi‐stable, exponential growth, linear growth, and nonlinear phases. The boundary layer is quasi‐stable near the subsolar point region. The K‐H instability starts at about 30° longitude, and grows exponentially with a spatial growth rate of 0.28∼0.87 RE−1until ∼45° longitude where the vortices fully develop. At larger longitudes, the instability grows linearly, while the vortices grow in size. From ∼80° longitude to the distant magnetotail, the K‐H instability develops nonlinearly and the vortices roll up. The wave frequency, wavelength, and phase speed are given at various spatial points. Model results show that the higher solar wind speed generates K‐H waves with higher frequency under the northward IMF, and the wavelengths and the phase speeds increase with the increase of the longitude. Moreover, we made a comparison of the K‐H wave periods on Earth's, Mercury's and Saturn's magnetopauses by a proposed prediction method.

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“…Therefore, the actual magnetospheric equilibrium state in such a case must be determined by solving where V is the unperturbed flow velocity equal to the E × B drift velocity. This equilibrium state is not a steady state, because it decays with a decay time constant τ d , which is given by Miura [1996] by where τ A = 2ℓ/ V A is the Alfvén transit time with 2ℓ being the field line length from the ionosphere in one hemisphere to the ionosphere in the opposite hemisphere and V A being the average Alfvén speed in the magnetosphere.…”

Section: Discussionmentioning

confidence: 99%

Pressure‐driven and ionosphere‐driven modes of magnetospheric interchange instability

Miura

2009

J. Geophys. Res.

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[1] A general stability criterion for magnetospheric interchange instability, which includes an ionospheric destabilizing contribution, is derived for an arbitrary finite-b magnetospheric model satisfying the magnetohydrostatic force balance. The derivation is based on the magnetospheric energy principle. Unperturbed field-aligned currents in finite-b nonaxisymmetric magnetospheric models are assumed to close via diamagnetic currents in the magnetosphere or in the ionosphere. By exploiting the limit of a very large perpendicular wave number and the eikonal representation for the perpendicular plasma displacement, the magnetospheric interchange mode is shown to be compressible. In this limit the kink mode makes no contribution to the change in the magnetospheric potential energy. By using magnetospheric flux coordinates, the explicit form of the magnetospheric potential energy change is calculated for interchange perturbations, which do not bend magnetospheric magnetic fields. For a nonaxisymmetric finite-b magnetospheric model, a combined effect of the pressure gradient and field line curvature, not only in the meridional plane but also in the plane parallel to the longitudinal direction, is responsible for pressure-driven interchange instability. For an axisymmetric, north-south symmetric and low-b magnetospheric model, in which the magnetic field is approximated by a dipole field, the m = 1 or m = 2 ionosphere-driven mode, where m is the azimuthal mode number, has an upper critical equatorial b value for instability in the order of 1. Thus a substantial region of the inner magnetosphere or the near-Earth magnetosphere may be unstable against ionosphere-driven interchange instability caused by a horizontal plasma displacement on the spherical ionospheric surface.Citation: Miura, A. (2009), Pressure-driven and ionosphere-driven modes of magnetospheric interchange instability, J. Geophys.

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Stabilization of the Kelvin‐Helmholtz instability by the transverse magnetic field in the Magnetosphere‐Ionosphere Coupling System

Cited by 17 publications

References 12 publications

MESSENGER orbital observations of large‐amplitude Kelvin‐Helmholtz waves at Mercury's magnetopause

MESSENGER orbital observations of large‐amplitude Kelvin‐Helmholtz waves at Mercury's magnetopause

Spatial distribution of Kelvin‐Helmholtz instability at low‐latitude boundary layer under different solar wind speed conditions

Pressure‐driven and ionosphere‐driven modes of magnetospheric interchange instability

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